subpages without the link.

With some of my XML changes, I have found that it would be really useful 
if \subpage didn't actually create a link, but just made the page a 
subpage silently, much like \ingroup does for Modules.

What would I need to do to add an alternative to \subpage that only 
links the page parent to child? I know enough about the backend system 
to make \subpage do it, but I know nothing about creating new commands.

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